Different acute effects of single-axis and multi-axis hand-arm vibration

Under laboratory conditions the effects of single-axis and multi-axis hand-arm vibration exposure on several strain parameters were tested in up to 20 male subjects. As parameters of these acute effects, the biodynamic vibration behavior of the hand-arm system, the electrical activity of the most affected muscle groups, the skin temperature, the vibration sensitivity of the fingertips, and the subjective vibration sensation were measured. When comparing simulated three-axis vibration exposure with single-axis vibration exposure, synergistic effects in the form of an increasing reaction could be found. It could be proven that the vector sum of the frequency-weighted acceleration in the three axes represents the acute effects better than does the weighted acceleration in the main axis alone. This summation has to take into account the relatively lower effects of vibration in the x- or y-direction compared with the z-direction. On the basis of the experimental results a new proposal for frequency weighting of the three different axes and an energetic summation procedure are derived. Application of this knowledge in the International Standard ISO 5349 is proposed.

Experience on the reversibility of the vibration-induced white finger disease

In connection with medical appraisements of the occupational disease No. 2104 "Vibration-induced vasospastic disease" 240 patients could be examined a first time, 94 of them a second time, 42 patients a third time and 11 patients a forth time. The interval between examinations was 2, 4 or 6 years respectively. The standard procedure besides clinical whole body examination included anamnestic questionnaire, cold-provocation test with infrared thermography and vibrotactile perception test. The evaluation of the diagnoses in principle followed the Stockholm vascular V and sensorineural SN stages and was used to establish the grade of disability for compensation. The re-examinations after 2-6 years gave information on the development of the health status after cessation of vibration exposure. In only about 54% of all cases there was any improvement, in 39% the health status was unchanged, in 7% aggravated. It is obvious that the reversibility of the VWF if any needs many years abstaining from vibration exposure.

The vibrotactile threshold (VT) at the fingertips of chain saw operators

The vibration sensitivity of the skin at the ten fingertips was tested with 72 chain saw operators examined due to VWF-disease and compared with controls. The vibrotactile perception threshold (frequency f = 125 Hz, load p = 1.3 N) proved to be 3 to 5 times as high for the exposed group compared to controls. There was no correlation between vibration sensitivity and peripheral circulation found in cold provocation test. Two different testing instruments (pallaesthesiometer = vibrotactometer) showed significant differences in results probably due to different technical details of the methods. It may be concluded that a standardization of the instrumentation and method is necessary for testing the vibrotactile perception threshold as a part of the nervous function in a comparable manner.

Medical and occupational preconditions for vibration-induced spinal disorders: occupational disease no. 2110 in Germany

The current state of scientific knowledge of the biodynamic behaviour of the vertebral column under the influence of whole-body vibration whilst sitting and results from epidemiological studies caused the medical board of experts on occupational health of the Federal Ministry of Labour in Germany to add a new occupational disease to the official list of occupational diseases. The occupational disease "diseases of the lumber spine from disc degeneration caused by long-term (mainly vertical) whole-body vibration exposure" has been introduced. The medical preconditions with the symptoms and the diagnostic methods are presented. With regard to the occupational preconditions for the acknowledgement of this occupational disease, a procedure is suggested which leads to the determination of the total occupational vibration exposure dose. Another requirement for recognition is that the chronic recurrent complaints have caused the patient to avoid any form of vibration exposure.

Effects of grip and push forces on the acute response of the hand-arm system under vibrating conditions

The purpose of the occupational medicine component of a joint research project was to study the effects of grip and push forces on the acute reaction of the hand-arm system under vibrating conditions. Several series of experiments were carried out by means of a vibration simulator in a laboratory environment in order to study biodynamic vibration behaviour, muscle response, skin temperature, shifts of the vibration perception threshold and the intensity of subjective vibration perception; in addition, field tests with hammer drills were conducted. On the whole, the findings obtained suggest that the coupling of the hand with the handle involved in using vibrating tools has a considerable impact on the stresses to which the hand-arm system is exposed. For this reason, future national and international rules and regulations on vibration assessment should take into consideration the effects of variations in coupling intensity.

Acute effects of transient vertical whole-body vibration

The question as to whether shock-type whole-body vibration causes increasingly acute strain was investigated. Random vibrations were superimposed with shocks differing in amplitude and in number per unit of time in a systematic manner. The weighted root mean square (rms) acceleration was kept constant in all over the varied experiments. A total of 17 men were exposed to vibration from an electrohydraulic simulator. The following strain criteria were used: biodynamic behavior of the trunk and the head, electrical activity of the muscles of the back and the neck, subjective sensation, skin temperature in the lumbar area and visual and tracking performance. It was found that increasing shock amplitude and, in some experiments, also increasing numbers of shocks led to increasingly acute effects that varied, depending on the kind of shock used. New methods should be developed for the assessment of transient vibration that are better than the existing standards.

[The effect of mechanical vibration on the spinal column]

Drivers of trucks, earth-moving equipment, fork-lift trucks, agricultural tractors and military vehicles are often exposed to a high amount of vibration. The stress-strain model is helpful for demonstrating the effects as the biodynamic behavior of the seated workers is important. Epidemiological research draws our attention to the danger involved for the lumbar spine from mechanical vibration. Prevention measures are given.

[Disorders in peripheral circulation and nerve function caused by working with hand-operated vibrating tools]

So far, there are only hypotheses about the etiology of vibration-caused vasospastic syndrome (VVS). When assessing the occupational stress, one must consider the kind, intensity and duration of the exposure to vibration, the static forces, environmental temperature, and noise. The symptoms peculiar to this disease are vasospastic attacks with white fingers, numbness and local pain. The diagnostic methods include a general medical examination, an anamnesis and special tests (cold provocation with measurements of finger-tip temperature or infrared thermography). Epidemiological research has enabled us to establish dose-effect relationship. Appropriate preventive measures may reduce the risk of VVS.

Biodynamic behavior of the trunk and the abdomen during whole-body vibration

Vibration strain may be defined as the sum of all reactions of the human being to vibration exposure. This also includes the biomechanical behavior of particular parts of the body. Knowledge about these reactions is necessary in the field of occupational health and ergonomics. Biomechanical models, experimental methods, and results are presented. It can be shown that under vibration exposure with different conditions (body posture, vibration direction), the body parts are in resonance at varying frequencies, mainly in a low frequency range.

Effects of combined hand-arm vibration and cold on skin temperature

Under laboratory conditions 14 healthy male subjects were exposed to hand-arm vibration (ahzw = 6.3 m/s2) at different air temperatures (5 degrees, 12 degrees, 18 degrees and 25 degrees C). Static load (grip force 15 N, push force 40 N) was kept constant. Finger tip temperature as an indirect criterion of the peripheral blood circulation was measured. As expected, low air temperatures (5 degrees, 12 degrees and 18 degrees C) cause a strong decrease of skin temperature. Under additional stress of vibration connected with static load, a further decrease of the mean skin temperature was noted. At this, static load proved to have a predominant influence on the acute diminution of skin temperature. The individual reaction to the stressors varied considerably. Field tests during practical work with a chain saw at low air temperatures showed results similar to those of the laboratory tests. The protective effect of a grip heating system could be demonstrated.

Thermographic assessment of skin temperature during a cold provocation test

A description was made of the development and application of infrared thermography and fingertip thermometry for the assessment of finger skin temperature during a cold provocation test. Three hundred and seventeen lumberjacks, grinders, metalworkers, stone cutters, and students were examined in laboratory and field investigations. Under laboratory conditions, the influence of water temperature and exposure duration was studied, and skin temperature measurements were made on the volar and dorsal side of the fingers. In the field occupational health examination, infrared thermography and fingertip thermometry were simultaneously applied during a cold provocation test. The following three types of temperature reaction could be recognized: normal rewarming and moderate delay and strong delay of rewarming. The temperature distribution along the finger length was analyzed. The following conclusions were drawn for practical application of the thermometric methods. Skin temperature must be measured on all 10 fingertips, either on the volar or on the dorsal surface. Fingertip thermometry may be used in occupational health examinations. Infrared thermography may yield more information on the development of disturbances in peripheral circulation along the finger length and may be used in special clinical work.

Whole-body vibration and disorders of the spine

This cross-sectional study is based on interviews and medical examinations of 352 operators of earth-moving machines who had been exposed to whole-body vibrations for at least three years. In addition, available X-rays showing different parts of the spines of 251 machine operators who had been exposed to vibration for at least ten years were used for evaluation. One hundred and forty-nine of the operators were asked about discomfort occurring immediately after an eight-hour work shift. The group of exposed persons was compared with a control group of 215 non-exposed persons. The percentage of subjects reporting spinal discomfort was much higher for the exposed group than for the non-exposed group. 68.7% of the operators complained of spinal discomfort in the lumbar spine, 6.8% in the thoracic column and 18.2% in the cervical column. The discomfort reported immediately after an eight-hour exposure to whole-body vibration was highly age-dependent. The epidemiological study resulted in an objective conformation of the spinal discomfort reported, 2/3 of which were related by the operators to the lumbar syndrome. Lumbar syndrome (81%) accounted for by far the highest number of spinal disorders. Examinations of the operators with at least ten years of exposure to whole-body vibrations showed that morphological changes in the lumbar spine occur earlier and much more frequently than in the case of non-exposed persons. Problems of etiology and pathogenesis are discussed.

Acute effects of shock-type vibration transmitted to the hand-arm system

The aim of the project was to find out whether shock-type vibration of hand-tools compared to non-impulsive vibration has stronger acute effects on the hand-arm system and therefore needs a stricter evaluation from the occupational health point of view in comparison with the requirements of the Draft International Standard ISO-DIS 5349. Under laboratory conditions, subjects were exposed to simulated vibration of hand-tools (grinder, chain saw, hammer-drill, pneumatic hammer, rivet hammer and nailer). The following evaluation criteria were used: biomechanical transmissibility of the hand-arm system (wrist, elbow joint, shoulder joint); muscle-activity (m. flexor carpi ulnaris, m. biceps, m. triceps); peripheral circulation (skin temperature) and subjective perception (comparison of intensity of standard and test vibrations). The results show no significant difference in acute effects on the hand-arm system between impulsive and non-impulsive type vibrations of the hand-tools tested with respect to the chosen vibration level, short-time exposure (up to 8 min) and evaluation criteria. In summary, therefore, it may be concluded that for the evaluation of shock-type vibration of the hand-tools tested, it is justified to use the existing Draft International Standard ISO-DIS 5349.

[Orthostatis stress from standing at work]

The evaluation of different body postures during work needs considering the interactions of anthropometric, physiological, orthopaedic, angiologic and biomechanical criteria on one side and of working conditons on the other. Many professions in industry as well as many tasks of the housewife still have to be done in standing position. But standing for long periods leads to increased strain of the bone and muscle system and to increased complaints and illness of the feet and legs. A comprehending catalogue of the effects of dominating standing posture and a catalogue of preventive measures are presented.

[Research on the biomechanical vibration behaviour of man's bulbi (author's transl)]

Mechanical vibration may lead to a decrease in visual performance. This may be expected if the natural frequency of the eye is excited. Experiments wit eight subjects and one repeat were carried out with the aim of calculating the biomechanical transmission of vibration between the cranium and the eye. The oscillation of the reflex-point of the cornea and of a light-point on the forehead were observed by a TV-camera and recorded using a multipoint-X-Y-tracker-system with a direct writer. The analysis showed typical resonance curves for the eye with maxima at 25-31.5 Hz typical to those found in animal experiments using other methods. Therefore at places of work transmission of such vibration frequencies to the head should be avoided to prevent a decrease in visual performance.

[Animal experiments on the biomechanical vibration behaviour of the bulbus (author's transl)]

Mechanical vibration may have a detrimental effect on visual performance. This particularly seems to be the case if the natural frequency of the bulbus is excited. Experiments with animals were made with the aim of calculating the biomechanic transmission of vibration between the cranium and bulbus. Postmortem experiments using pig crania have shown that in vivo application of the method of sewing miniature accelerometers onto the cornea may be possible. Our experiments with monkeys gave typical resonance curves for the transmission of vibration of the bulbi with maxima between 25 and 31.5 Hz. Transferability of the results to the human eye is discussed.

[Mechanical factors contributing to the cause of retinal detachment (author's transl)]

There is no doubt that besides the anatomical changes in vitreous and retinal structures mechanical factors are involved in producing retinal detachment. Especially vertical accelerations can produce fast movements of the vitreous, which also can induce the retina. To investigate the effect of various external movements upon the eye a number of experiments were made: 31 variations of movements with and without different vehicles at different speeds have been investigated. As direct measurements of acceleration of the eye are not possible at present, the upper verges of the orbitae were chosen as measuring point. Additionally accelerations were measured nearest to the place of the entrance of vibration to the body in order to examine the transmissibility of vibration to the orbita. The transduced signal of the accelerometer was recorded on a tape. When measuring in vehicles or riding, radiotelemetry of the signal was used. The statistical analysis of the results was performed. Typical frequencies were found in which the amplitude of the induced acceleration even is enlargen on its way through the body to the orbita. The significance of the different results for producing dangerous mechanical stress to the eye is discussed.